It is a little over half a century since Eric Hobsbawm, the intuitive pattern-maker of modern history, gave his first lecture at Birkbeck College in London. When he returns tomorrow evening to deliver the college's 175th anniversary talk, there will be something of a sense of a circle closing, and ironies that will not be lost on him.

The subject of Hobsbawm's address is 'Birkbeck and the Left', but five decades ago his radical socialism almost kept him out of university life altogether. A lifelong member of the Communist Party, he suggests that he got in to academia 'under the wire'; a year later, after the Berlin Airlift in 1948, his story, he believes, would have been markedly different. As it was, partly because of his political affiliations, he did not get promotion to a professorship until 1970.

He has never needed any lessons, however, in the virtues of playing a long game. His landmark trilogy on the nineteenth century synthesised myriad competing social swells into great epochal waves: the Ages of Revolution, and of Capital, and of Empire. He has characterised his own time and tide as the Age of Extremes, the tempestuous force of which conspired to deposit him on the shore of the present as the Last Marxist; still, he refuses to believe himself beached. One old friend observes: 'Eric has long ago worked out his precise intellectual position and he's quite happy there, thank you very much.'

Talking to Hobsbawm now, at 83, his mind still in edgy overdrive, his body language made for compelling awkwardness, you have a strong sense of the history that he has measured on his own pulse. He was born in Alexandria to a middle-class Jewish family in the year of the October Revolution, 1917, and he has lived to see the full tragic narrative of the Bolshevik utopia unfold. It is characteristic of him that he remains sentimental about its origins, but clear-eyed over its outcome.

Before the war, his family moved first to Vienna and then to Berlin, where Hobsbawm came of age. He says he still recognises in himself the kernel of the 14-year-old boy who read on a newspaper board the headline announcing the accession of the Third Reich. 'Anybody who saw Hitler's rise happen first-hand could not have helped but be shaped by it, politically,' he says now. 'This is still there in me. That boy is still somewhere inside, always will be.'

Hobsbawm's parents both died during the Depression and he and his sister were taken in by his uncle, who worked for a Hollywood firm in Berlin. Almost immediately, the family moved to England, following his uncle's job, and for three years, Hobsbawm experienced what he has rarely felt since - that history was happening without him. He was bored and dislocated by the transition from the intensities of pre-war Germany to the complacencies of a south London grammar school. It was not until he got to Cambridge that he sensed he could carry on with the conversations that he'd started in Berlin.

Hobsbawm has defined and explained the progress of the last century as mankind learning to 'live in expectation of apocalypse'. He responded to those intimations in himself by joining the Communist Party. He would, he says, certainly have become a member earlier, but that his uncle was 'rather stiff' on the subject. 'He used to say, "You kids don't know what you are letting yourselves in for".' Hobsbawm smiles now, seeing his life unspooling in that prophecy. 'He was right, of course.'

You could imagine that the gangling young émigré, uprooted and orphaned, might have been attracted to the certainties of the party as a surrogate family and consequently begin to explain the strength of the attachment as a powerfully emotional as well as an intellectual one. Looking back, he suggests that 'probably that kind of security was one of the appeals', but also that he 'never felt short of family... it was more that you just felt things were going to pieces, and you felt it needed a revolution to re-create it, to put it back together'.

After the war, these political commitments no longer seemed quite so innocent. Hobsbawm applied for a series of Oxbridge jobs, and was 'turned down right, left and centre' He fetched up instead, happily, at Birkbeck, and found inspiration in the radicalism of J.D. Bernal, the maverick Marxist and physicist, 'by far the brightest man there, who looked like a sea captain with long, bushy hair, and who walked, as he said, like the pobble who had no toes'. In some ways, Hobsbawm still views the world as the semi-detached, cold warrior he was then, or at least the legacy of that rhetoric continues to inflect his memories. 'Of course, physics tended to be very Left,' he will say, recalling old common-room divides, 'and obviously so did crystallography'; or, speaking, of one mathematician colleague: 'I'm not sure if he didn't become a Maoist at about that time...'

One of his friends of that era at Birkbeck, Barbara Hardy, now Professor of English, remembers Hobsbawm in his late thirties, as 'very sexy and amusing, and wonderfully candid'. Lectures at Birkbeck, whose student body is part-time, are in the evenings and the challenge among the faculty was to keep its audience awake in the graveyard slot between eight and nine. Hobsbawm, by all accounts, achieved this effortlessly and sustained his intellectual energy after hours. 'When Eric was around there was always conversation,' recalls Hardy, suggesting that so much sherry was drunk in those days that she can now no longer look a glass of it in the eye.

There would be sudden jaunts to Ronnie Scott's (Hobsbawm was at the time an impassioned jazz critic for the New Statesman) or on, one occasion, she recalls, to listen to Billy Graham. 'Eric always wanted to be seeing something new,' she says, 'or to know something new. He was always fully engaged.'

Throughout this period, Hobsbawm maintained his commitment to communism, a fact which some of his colleagues, including Hardy, found, at best, mysterious. Though he never proselytised unlike many of his comrades, Hobsbawm did not leave the party after 1956. His concession was to argue that even the most monolithic members had, given events, to 'reconsider the equation: party = life'.

Hobsbawm appears to have resolved that equation for himself in part by pursuing a more limited kind of personal utopia. His standing in Central Europe and Latin America as an 'important revisionist' allowed him the freedom to travel and establish a network of friends, who later became regular visitors to his home on the flanks of Hampstead Heath. There were - are - dinners at which British intellectuals could find themselves outnumbered by German publishers, Czech historians and Latin American novelists. The driving force of north London's most distinctive Central European salon is Marlene, Hobsbawm's second wife, who, friends say, 'provides this remarkable gregarious atmosphere around him'. One regular recipient of this hospitality, Neal Ascherson, says: 'Eric is still very much a Fifties bohemian, in a way. He loves, say, the idea of some weird drink brought back from Slobodnia in an odd -shaped bottle. You have to watch yourself or you are falling over before the food arrives.'

In part, this stubborn microcosm of conviviality explains why Hobsbawm has kept the faith. As the walls were coming down in 1989, Hobsbawm was often asked to explain his continued commitment. Typically, he replied both as a conviction historian - 'I think the movement has achieved at least one absolutely major thing, and that includes the Soviet Union, namely the defeat of fascism,' - and as a rose-tinted loyalist: 'I don't wish to be untrue to my past or comrades of mine, a lot of them dead, some of them killed by their own side, whom I've admired [as] models to follow, in their unselfishness.'

The end of the Cold War and the new public relations-led world order that followed brought to a close Hobsbawm's particular influence over more domestic battles, too. In the Eighties, he had become the unofficial philosopher and intellectual conscience of the Labour Party as it fought for its soul and its future under Michael Foot and Neil Kinnock. But if he despairs of the present government, he tends to keep his counsel or employs a Zhou Enlai defence that it is 'too early to tell'. Though he concedes that Blair's populist anti-intellectualism 'gets on his wick', he can laugh when he says he 'finds it hard to envisage not voting Labour, put it that way'.

If Hobsbawm is saddened by the way things have turned out, he has enough professional detachment not to let it show. Having lived to tell the lucid tales of the past two centuries, he approaches the new one, the subject of his most recent, prophetic, book, with few grounds for optimism, but with great vigour. One of the antidotes to discontent for Hobsbawm has always been industry and he shows no signs of slacking. He regrets that recently he has had to cut back on his globetrotting - only 'a few trips to Europe and South America' - in order to concentrate on writing his autobiography. He hopes, he says, with some understatement, that it will describe 'different countries, what I know of 'em, how I got to know 'em, that kind of stuff'. Though he'll never make a blurb writer, you guess that, for some at least, it will be the essential Baedeker to the century.